44 
Fishery Bulletin 110(1) 
mental differences, the relationship between maternal 
size and age and larval quality found in rockfish off the 
U.S. west coast may not be applicable to rockfish species 
off the coast of Alaska. 
Age and size truncation of a population, i.e., a sharp 
decrease or absence of older, larger fish, is common in 
an exploited population and should be considered in 
management of fish stocks. Truncation of a rockfish 
population, in which parturition timing is related to 
age or size, could result in a shorter parturition season. 
Therefore, a size or age truncated population is less 
resistant to annual environmental fluctuations of larval 
food availability (Berkeley et al., 2004b). Because sum- 
mer is shorter in Alaska than on the U.S. west coast, 
there are likely increased advantages to parturating 
precisely when larval food is available so that larvae 
can begin growth as soon as possible. Fish at northern 
latitudes may therefore be more likely to exhibit ef- 
fects of age or size on developmental timing. Because 
quillback rockfish in this study exhibited evidence of 
age- and size-dependent parturition timing, they are 
likely vulnerable to potentially deleterious effects of age 
or size truncation. 
Conclusion 
Current management practice is to assume equal repro- 
ductive success based on the biomass of mature fish 
and does not account for variability in success based on 
maternal age or size. Incorporation of maternal effects 
on productivity into population models for Alaska Pacific 
ocean perch causes a decrease in the fishing rate asso- 
ciated with management reference points such as F 
(the fishing rate associated with maximum sustainable 
yield) and F 40% (the fishing rate that conserves 40% 
of the reproductive output produced per recruit for an 
unfished population) (Spencer et ah, 2007). Further 
studies of maternal effects on larval quality, parturi- 
tion timing, fecundity, and population recruitment are 
recommended for other rockfish species in Alaska. Spe- 
cies subject to higher exploitation rates than those for 
quillback rockfish may be at greater risk of age or size 
truncation and potentially a decrease in productivity. In 
this case, a more conservative harvest would be needed 
to avoid population declines. 
Acknowledgments 
We thank J. Heifetz, P. Rigby, P.-J. Hulson (all from 
the Alaska Fisheries Science Center, AFSC) for helpful 
reviews on earlier versions of this manuscript. P. Spencer 
(AFSC) provided much appreciated reviews and advice 
throughout writing. We also thank J. Heifetz, K. Shot- 
well (AFSC), and F. Sewall (University of Alaska Fair- 
banks) for assistance in the field. We greatly appreciate 
B. Goetz (AFSC, Age and Growth Laboratory) for read- 
ing ages from otoliths. We thank the maintenance and 
science staff at the AFSC Little Port Walter research 
station for assistance with vessels, transportation, and 
sampling equipment. 
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